What is the basic function of a megger?

Answer 1

On the whole megger testing is non destructive. What happens is a DC voltage is applied to the device or winding under test. It is an insulation test to see is the insulation has been injured in any way to cause a short circuit when normal power is applied to it. On my megger there are 3 ranges 300V, 750V, and 1000 volts. Applying the proper voltage is essential to not damaging the device you are testing. Working voltages up to 240 volts should use the 300 range. Working voltages up to 600 volts use the 750 volt range and working voltages above 600 use the 1000 volt range. As you can see if you used the 1000 volt range on a device that had a working voltage of say 24 volts you could damage the insulation just by testing it. So meggering a device is non destructive if you use the tester as its instructions tell you to.

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Answer 2

A Megger is a device that will test the insulation of the circuit it is connected to. It produces a DC voltage to check for leakage current from the conductor to ground. It then will give you the value of insulation in Mega Ohms. Generally anything less than one Mega Ohm per thousand volts is poor insulation. Be careful when using this device because it does produce high DC voltages and it can give you an awakening jolt. It is most commonly used to test the insulation in motors and generators but can be used in many other applications.

Note that the word "Megger" is actually a trade name (hence capital M). The generic name for such an insturment is "high-voltage insulation tester".

Although Mega Ohms is strictly correct, you'll most often hear it pronounced rather more easily as "Meggohms".